Fractal root system of Melica przewalskyi along different aspect in degraded grassland

Aims Fractal root system is phenotypic plasticity result of plant root architecture to respond to environmental heterogeneity, may reflect the growth strategy of plants to adapt to environmental conditions. Our objective was to explore the relationship between root fractal dimension and fractal abundance of fractal root system of Melica przewalskyi population in response to aspect variation in the northwest of China. Methods The study site was located in a degraded alpine grassland on the northern slope in Qilian Mountains, Gansu Province, China. Survey and sampling were carried out at 40 plots which were set up along four slope aspects transects with 20 m distance between adjacent plots. Handheld GPS was used to determine the elevation, longitude and latitude of each plot. ArcGIS was used to set up digital elevation model (DEM). Community traits were investigated and six individuals roots of M. przewalskyi were collected randomly at each plot. The samples were cleaned and divided into different organs, then scanning the root with the Win-RHIZO for measurements of fractal dimension and fractal abundance in laboratory, and their biomass were then measured after being dried at 80 °C in an oven. Important findings With the slope aspect turned from north to east, west, and south, the density, height and soil moisture content of the plant community displayed a pattern of initial decline, the height, density, root fractal abundance of M. przewalskyi increased and the root fractal dimension decreased. The root fractal dimension was negatively associated with the fractal abundance in all aspects, but the relationship varied along the slope aspects gradient; there was a highly significant negative correlation (p < 0.01) between the root fractal dimension and fractal abundance at north slope and south slope aspect, whereas the correlation only reached a significant level (p < 0.05) at the east slope aspect and west slope aspect; indicating that there is a trade-off between the root fractal dimension and fractal abundance. In addition, when the slope aspect changed from north to east, west and south, the standardized major axis (SMA) slope of the regression equation in the scaling relationships between root fractal dimension and fractal abundance increased (p < 0.05), indicating that the roots of M. przewalskyi at the droughty southern slope have less branch and more sparse in the same soil volume of root exploitation and utilization. Consequently, the resource allocation pattern on reasonable trade-off between root fractal dimension and fractal abundance in different slope aspect of M. przewalskyi, reflects the relationship between the income and the cost of construction of plant root architecture.     

Neural inhibition sharpens auditory spatial selectivity of bat inferior collicular neurons

This study examines the role of neural inhibition in auditory spatial selectivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus, using a two-tone inhibition paradigm. Two-tone inhibition decreases auditory spatial response areas but increases the slopes of directional sensitivity curves of inferior collicular neurons. Inferior collicular neurons have either directionally-selective or hemifield directional sensitivity curves. A directionally-selective curve always has a peak which is at least 50% larger than the minimum. A hemifield directional sensitivity curve rises from an ipsilateral angle by more than 50% and either reaches a plateau or declines by less than 50% over a range of contralateral angles. Two-tone inhibition does not change directionally-selective curves but changes most hemifield directional sensitivity curves into directionally-selective curves. Auditory spatial selectivity determined both with and without two-tone inhibition increases with increasing best-excitatory frequency. Sharpening of auditory spatial selectivity by two-tone inhibition is larger for neurons with smaller differences between excitatory and inhibitory best frequencies. The effect of two-tone inhibition on auditory spatial selectivity increases with increasing inhibitory tone intensity but decreases with increasing intertone interval. The implications of these findings in bat echolocation are discussed. Accepted: 18 January 2000     

The fecundity patterns of S and L type rotifers of Brachionus plicatilis

Fecundity patterns of S and L type rotifers Brachionus plicatilis, which were previously found to have distinct growth ability, were analyzed using data of age-specific fecundity. The data were obtained by individual cultures of S and L type strains at 17, 24 and 34 °C. The pattern was analyzed by using normal probability functions. When the age was transformed into logarithmic value, the S and L types had an identical pattern of fecundity at every temperature. This fact indicates that the difference of the growth response to the temperature between S and L type strains stemmed only from the differences in net reproduction rate, not from the pattern.     

Feedback inhibition of sodium uptake in K+-depolarized toad urinary bladders

Ouabain-blocked toad urinary bladders were maintained in Na⁺-free mucosal solutions, and a depolarizing solution of high K⁺ activity containing only 5 mM Na⁺ on the serosal side. Exposure to mucosal sodium (20 mM activity) evoked a transient amiloride-blockable inward current, which decayed to near zero within one hour. The apical sodium conductance increased in the initial phase of the current decay and decreased in the second phase. The conductance decrease required Ca²⁺ to be present on the serosal side and was more rapid when the mucosal Na⁺ activity was higher. At 20 mM mucosal Na⁺ and 3 mM serosal Ca²⁺ the initial (maximal) rate of inhibition amounted to 20% in 10 min. The conductance decrease could be accelerated by raising the serosal Ca²⁺ activity to 10 mM. The inhibition reversed on lowering the serosal Ca²⁺ to 3 μM and, in addition, the mucosal Na⁺ to zero. Exposure of the mucosal surface to the ionophore nystatin abolished the Ca²⁺ sensitivity of the transcellular conductance, showing that the Ca²⁺-sensitive conductance resides in the apical membrane. The data imply that in the K⁺-depolarized epithelia, cellular Ca²⁺, taken up from the serosal medium by means of a Na⁺-Ca²⁺ antiport, cause feedback inhibition by blockage of apical Na⁺ channels. However, the rate of inhibition is small, such that this regulatory mechanism will have little effect at 1 mM serosal Ca²⁺ and less than 20 mM cellular Na⁺.     

Downhill movement of litter and its implication for ecological studies in three types of forest in Japan

The amount of litter moving down the slope was measured in three types of forest, together with an examination of rain as a factor in bringing this about. The three forest types were a natural mixed stand ofPinus densiflora and hardwood trees (plot A), aCryptomeria japonica plantation (plot S) and aChamaecyparis obtusa plantation (plot H). The amount of moved litter was quite large in plots A and H, but relatively small in plot S. The rain factor had little influence on litter movement in plot A, but was the main cause of movement in plot S and (especially) plot H. It is suggested that measurement of litter input and output not only by traps above ground level, but also by ones on the ground is essential for determining the cycling of elements inC. obtusa forests. It is also suggested that the decomposition of leaf litter should be studied both on the soil surface and in the soil inC. obtusa forests.     

1980—2018年祁连山南坡土地利用变化及其驱动力

祁连山是我国第一阶梯和第二阶梯的分界线,生态环境脆弱,对过渡地带土地利用变化及其驱动力研究具有重要的生态意义。本研究以祁连山南坡为研究区,基于1980—2018年遥感影像数据,运用空间自相关分析法、ArcGIS空间分析方法和主成分分析法分析了土地利用的时空变化特征及其驱动力。结果表明: 1980—2018年,草地是研究区土地利用类型的主体,建设用地所占比重最小,水域、草地表现为下降趋势,未利用土地、建设用地和耕地均呈现出增长态势,林地变化较小。不同地类单一土地利用动态度从大到小依次为:建设用地＞水域＞耕地＞未利用土地＞林地＞草地,综合土地利用动态度为0.9%。不同土地利用类型空间分布表现出空间集聚性特征。耕地增加的区域和林地、草地减少的区域主要分布在门源县城所处大通河谷地西北侧,天峻县东北部大通河上游地区存在工矿建设用地占用草地的现象。土地利用变化驱动力主要为人口数量、科技、城市化、经济发展水平和政策。本研究结果可为政府合理规划和利用土地资源提供依据,对祁连山南坡生态环境保护和社会经济可持续发展具有重大意义。     

坡向和坡位对四川夹金山灌丛群落结构与物种多样性特征的影响

研究不同坡向、坡位夹金山灌丛群落结构和物种多样性特征。结果表明: 在 24 个样地中,共有维管植物 186 种,隶属于 50 科 127 属。其中,灌木层有 32 种,隶属于 14 科 22 属,阴坡下坡位物种数最多;草本层有 154 种,隶属于 43 科 109 属,阴坡物种数最少。灌木层的平均高度表现为阳坡>半阳坡>阴坡,平均密度则相反;草本层平均高度表现为阴坡>半阳坡>阳坡,平均密度无显著变化。坡位仅对阳坡草本层平均高度有显著影响,灌木层物种多样性在阴坡较高,草本层物种多样性在阳坡下坡位和阴坡中坡位较高。坡向对灌木层和草本层 Shannon多样性指数、Simpson优势度指数、物种丰富度指数、Pielou均匀度指数影响显著(除草本层 Simpson 指数),坡位对灌木层和草本层物种多样性指数均无显著影响,坡向和坡位的交互作用对草本层物种多样性的影响大于灌木层。冗余分析(RDA)表明,物种多样性不仅与坡向正弦值、坡向余弦值相关,也与群落结构特征相关性较大。     

西双版纳国家级自然保护区蚂蚁-树互作网络空间变异

网络分析(network analysis)可以同时分析群落中的物种多样性和种间关系, 为了解生态群落的稳定性机制提供了新的分析思路和方法。本研究从西双版纳国家级自然保护区的纳板河、勐仑和勐腊(补蚌)三个地点采集了树栖性蚂蚁及树木的种类和数量数据, 对蚂蚁-树组成的二分网络进行了分析, 探讨了3个采样点物种的多样性、网络指标以及群落指标之间的关系。我们采用零模型的方法比较了3个样点的标准化网络参数差异。结果表明: 蚂蚁和树木的物种数以及树的异质性指数(Shannon-Wiener多样性指数、Simpson多样性指数)都呈现出勐仑 > 纳板河 > 补蚌的趋势。树木-蚂蚁的灭绝曲线系数大小关系同样为勐仑 > 纳板河 > 补蚌, 灭绝曲线与树的物种数及异质性指数大小趋势一致, 而与蚂蚁的异质性指数并不吻合。根据Z值的绝对值来看, 网络参数(加权嵌套性、平均连接数、特化水平、模块性、连接度)与群落参数(灭绝曲线系数、生态位重叠)的大小趋势相同, 表现出勐仑 > 纳板河 > 补蚌的趋势。综上所述, 蚂蚁-树互作网络的稳定性(灭绝曲线系数)主要由树的数量和异质性指数决定。网络的加权嵌套性和网络中节点的平均连接数也能促进群落的稳定性。而在一个特化的(数值越大表示专性互作越多)和模块化(具有较多密切互作的节点单元)的网络中, 当低营养级物种灭绝时高营养级物种数量将迅速减少。     

Seed germination and plant fitness response of a narrowly endemic,rare winter annual to spatial heterogeneity in microenvironment

Environmental heterogeneity affects distributions of plant species, although the effects of fine-scale heterogeneity on plant demographies are not widely studied. Diminutive winter annuals, especially rare taxa, can be sensitive to spatial variation in microenvironment as a consequence of their small stature above and belowground. To address whether spatial environmental heterogeneity affects demography, germination and fitness of Chorizanthe orcuttiana, an endangered winter annual distributed in distinct easterly and westerly microhabitats within an exceedingly narrow niche in California, we performed multiyear observational and empirical studies. We manipulated after-ripening environment, soil moisture and ambient light at both aspects, and profiled microclimate, soil physicochemistry and soil microbiomes at all sites. We show that easterly aspects host larger plants in larger populations, and have lower air temperatures combined with higher soil moisture in comparison to the west-facing sites. Yet, soil physicochemistry and microbiomes were similar across all sites. Manipulations of after-ripening conditions showed that seeds exposed to low humidity (17%) during dormancy and sown at easterly aspects exhibited the highest germination percentages, whereas seeds incubated in situ and subsequently sown at westerly aspects yielded the lowest germination. Simultaneous manipulations of soil moisture and light showed that at both aspects higher moisture combined with shade led to higher germination, whereas ambient soil moisture combined with shade yielded the lowest germination. Altogether, our studies show that the diminutive, rare winter annual C. orcuttiana exhibits higher germination and plant fitness under cooler soil conditions with higher soil moisture while preferring drier environments during after-ripening.     

露天煤矿排土场边坡植被组成特征及其群落稳定性评价

研究植被恢复过程中植物群落组成、结构及稳定性的变化,可进一步了解到植物群落的演替过程及规律。采用空间代时间的方法对内蒙古锡林郭勒盟北电胜利露天煤矿4个排土场边坡人工恢复植被进行群落调查,在此基础上采用多样性指数与优化后的M.Godron稳定性指数对植物物种组成、物种多样性及其群落稳定性进行分析,探究不同恢复年限排土场边坡植被在恢复过程中群落特征及稳定性变化特征。结果表明：（1）排土场边坡植物物种组成共有16科44属56种,植物群落组成较简单,其中禾本科种类最多,生长型以草本植物为主。（2）随着恢复年限的增加,植物生活型由一、二年生转变为多年生,坡面优势种由人工种植植物转变为本土植物。（3）整体看,随着恢复年限增加,物种多样性呈下降趋势,群落稳定性整体呈上升趋势。（4）由于不同坡向土壤微环境差异,北坡恢复效果及稳定性好于南坡。本研究在一定程度上可为露天煤矿排土场边坡人工修复过程中植物物种及合理配置模式的选择提供科学依据。